White light emitting LEDs (“white LEDs”) include one or more photoluminescence materials (typically inorganic phosphor materials), which absorb a portion of the blue light emitted by the LED and re-emit light of a different color (wavelength). The portion of the blue light generated by the LED that is not absorbed by the phosphor material combined with the light emitted by the phosphor provides light which appears to the eye as being white in color. Due to their long operating life expectancy (>50,000 hours) and high luminous efficacy (100 lm/W and higher) white LEDs are rapidly being used to replace conventional fluorescent, compact fluorescent and incandescent lamps. LED lamps (bulbs) are typically constructed from a small number of high-intensity white LEDs.
Recently, LED-filament lamps have been developed that comprise LED-filaments that closely resemble the filament of a traditional incandescent lamp. The LED-filaments, which are typically about an inch long, comprise COG (Chip-On-Glass) devices having a plurality of low-power LED chips mounted on a light-transmissive (transparent) glass substrate. The LED-filaments are encased in a phosphor-impregnated encapsulant, such as silicone. Typically, LED-filament lamps are configured to generate “warm white” light with a CCT (Correlated Color Temperature) of 2700 K to 3000 K with a General Color Rendering Index (CRI Ra) of up to 80. A need exists for LED-filament lamps having a CRI Ra of at least 90. While the CRI Ra of white LEDs can be increased by including an orange or red emitting phosphor, it is found that the luminous efficacy decreases. There is a need to provide an LED-Filament lamp that has a CRI Ra of 90 and which has a smaller decrease in luminous efficacy compared with packaged white LEDs.